High-power surge arrester



March 4, 1969 M. E. HALE ET AL 3,431,452

HIGH-POWER SURGE ARRESTER Filed May 17, 1967 INVENTORS #01984) E. #JLE R055?! D. W /6' United States Patent 3,431,452 HIGH-POWER SURGE ARRESTER Murray Everett Hale, Atkinson, N.H., and Robert David Wright, Canton, Mass., assignors t0 the United States of America as represented by the Secretary of the Air Force Filed May 17, 1967, Ser. No. 640,461 U.S. Cl. 313-231 Int. Cl. H01j .17/26, 61/28 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to surge arresters and more particularly to a high-power electrical surge arrester stabilizing the breakdown conditions thereof.

The present invention effectively stabilizes the breakdown conditions of a high-power electrical surge arrester, i.e. if the typical 60 cycle or DC breakdown has a nominal value of 400 volts, the arrester always breaks down at 400 volts regardless of the time elapsed since the last breakdown or the rise time of the applied voltage.

The prior art methods have included the use of Ni-63 or Krypton 85 within the gap of the surge arrester as radioactive keep alive agents; i.e., they maintain a certain level of ionization at all times within the unit to provide initial electrons for fast breakdown of the gap when its breakdown is exceeded. Another method uses a titania (TiO between an auxiliary set of electrodes to provide UV irradiation of the main gap of the surge arrester on application of an impulse to make the breakdown of the main gap faster.

In the radioactive case the level of radiation that must be maintained to provide a significant advantage is so high as to constitute a hazard, at least psychologically. No unit using this method has been observed to depart drastically from the normal behavior without trace elements. In the case of the present invention, the present use depends on a separate TiO structure within the gap envelope and depends on magic properties of T102.

Operation of the device of the present invention depends on the electron emissive properties of various agents which may be used to coat the inner wall of the ceramic shell of the surge arrester gap. Bi'eakdown of the gap is initiated by the fact that due to the small gap spacings (or vacancies in the case of T102) in the coating, many areas of the coating become electron emissive immediately on application of a rising voltage at the electrodes.

An object of the present invention is to provide a highpower surge arrester designed to breakdown with minimal time lapse at a predetermined voltage level.

Another object of the present invention is to provide a high-power surge arrester wherein an avalanche type of breakdown is initiated therein.

Yet another object of the present invention is to pro vide a high-power surge arrester wherein breakdown occurs therein at a predetermined voltage level regardless of the time elapsed since the last breakdown or rise time of the applied voltage.

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description when taken in conjunction with the accompanying drawing illustrating one embodiment of the present invention.

Now referring to the single figure of the present invention, there are shown electrodes 10 and 11 which are pressure fitted and sealed into ceramic shell 12. Electrodes 10 and 11 are separated a predetermined distance for breakdown at a predetermined voltage, for example, 400 volts. Electrodes 10 and 11 receive input surging voltages. Supporting metal structure 13 is also provided for ceramic shell 12. Annular glass ring 15 clamps onto and seals shell 12 to form a vacuum tight fitting. Supporting structure 13 and ring 15 are integrated. Shell 12, supporting structure 13 and ring 15 provide a housing for electrodes 10 and 11. This housing may also be referred to as the gap housing or envelope. Up to this point, the surge arrester is of conventional structure.

The inner wall of ceramic shell has applied thereto coating 14. The coating may be deposited by conventional methods such as spraying and baking, etc., and can be composed of carbon particles TiO as an N type semiconductor or can becomposed of metallic particles. Such a coating can be DC or AC coupled to the electrodes. In the present instance, it is AC coupled. Since the impedance of the coating is so high, AC coupling is effective to fairly low frequencies even if no effort is made to purposely introduce it, the stray capacitance being adequate. It is to be noted the electrodes and the intervening space therebetween is referred to as the main gap.

With a 60 cycle or 'DC breakdown value of 400 volts, for example, the arrester always breaks down at 400 volts regardless of the time elapsed since the last breakdown or the rise time of the applied voltage.

Breakdown of the gap is initiated by the fact that due to the small gap spacings (or vacancies in the TiO in the coating, many areas of the coating become electron emissive immediately upon the application of a rising voltage at the electrodes. Without introducing acceleration effects, the drift velocity of a few of the electrons is fast enough for them to be in the area of the main gap in some tens of nanoseconds. These provide the initial electrons needed to start an avalanche breakdown in the main gap. The whole process requires less than nanoseconds under reasonably fast impulse conditions and also is very fast for incoming rise times comparable to 60 cycles AC. With the above process, it is possible to specify a surge arrester that has a DC to impulse breakdown ratio of unity.

In the alternative the whole gap shell could be made out of TiO suitably treated to become a very high impedance semiconductor.

While a particular embodiment of the invention has been shown and described, modifications may be made. It is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A high-power surge arrester having a stabilized predetermined breakdown voltage level comprising a pair of 3 4 electrodes receiving surging and rising voltages and be- 4. A high-power surge arrester as described in claim 2 ing spaced a predetermined distance in accordance with wherein said coating is DC coupled to said electrodes. said bIBakdFWII voltage level, an lenvelope surrounding References Cited said pair 0 electrodes, said enve ope having an inner wall, and a coating of TiO on said inner wall, said coat- 5 UNITED STATES PATENTS ing operating as an N type semiconductor and becoming 2,449,397 9/ 1948 Lamphel'e 3 electron emissive immediately on application of a ris- 3,154,718 10/1964 Yonkers et 313325 X ring voltage at said electrodes JOHN W. HUCKERT, Primary Examiner.

2. A high-power surge arrester as described in claim 1 wherein said envelope is comprised of a ceramic shell. 10 POLISSACK Assistant Exammer' 3. A high-power surge arrester as described in claim 2 S. Cl. X.R. wherein said coating is AC coupled to said electrodes. 313313, 325; 315-35; 3l7-61 

